The present invention relates to the art of induction heating and, more particularly, to an inductor for use in connection with the induction hardening of metal workpieces.
The inductor of the present invention finds particular utility in connection with the heating and hardening of hollow automotive wheel spindles having axially extending sections of different radial thickness, and the invention will be disclosed and described in detail herein with regard to such a workpiece. At the same time, however, it will be appreciated that the present invention is applicable to the induction heating of workpieces other than wheel spindles and is applicable, in general, to workpieces having axially extending surface portions of different dimensions laterally of the surface and with respect to which it is desired to achieve a uniform depth of heating along the axial surface.
As is well known, an automobile wheel spindle is a tubular metal member having an axially extending outer surface which is adapted to receive and support wheel bearing components and a vehicle wheel. Such a spindle has axially adjacent areas in which the outer surface is radially stepped, whereby the radial wall thickness of the spindle varies from one axial section to the next. For well known reasons, it is necessary to harden the axially extending outer surfaces of the spindle, such as by inductively heating the spindle and then flowing a quenching liquid onto the heated surface. Such a spindle additionally includes a flange extending radially outwardly from the inner end of the axially extending surface portion of the spindle, and it is also necessary to extend the area of hardening from the inner end of the axially extending surface portion radially outwardly a short distance into the flange.
Inductors heretofore employed in connection with the induction hardening of such spindles, and other workpieces having surface variations of the character providing different workpiece dimensions transverse to the outer surface, have not enabled achieving a uniform depth of the heating pattern inwardly of the outer surface from one axial section of the workpiece to the next, and/or have not enabled induction heating of the workpiece to be achieved efficiently. In this respect, for example, certain inductors heretofore provided have been inclined relative to the total axial length of the surface to be hardened and this relationship, for each axial section, provides for the inductor to be closer to the workpiece at one end of the axial section than at the other end. Accordingly, when the inductor is magnetically coupled with the workpiece the air gap between the inductor and workpiece varies along the length of a given axial section of the workpiece, whereby the depth of the heat pattern is greater at one end of the axial section than the other. Other efforts have included scanning the workpiece with an inductor coil having a fixed diametrical relationship with respect to the workpiece. While this may provide for a desired depth of heat pattern along one axial section of the workpiece, the several axial sections are radially stepped relative to one another. Thus, the air gap from one section to the next will change and the depth of the heat pattern in adjacent sections will vary accordingly. Another problem encountered in connection with obtaining a uniform depth of heat pattern results from the fact that the different axial sections of the workpiece have different circumferences. Thus, a given speed of relative rotation between the inductor and workpiece to achieve the desired depth of heat pattern in one section will not provide the same depth in the other sections which have a different circumference from the one section.